The AK-47 changed the face of armed conflict, and its appeal among soldiers and civilians alike is based in solid engineering and design practices.

The Avtomat Kalashnikova (AK) assault rifle has a well-documented reputation as an influencer of world conflicts since Mikhail Kalashnikov's brainchild entered service with the Soviet army in 1949. However, while the original AK-47 is often cited as a triumph of form following function, the influence of its development and design ethos on engineering in general has been less well recognised.

The changed nature of ground combat in the Second World War had shown that the kinds of firearms traditional to European armies were proving unsuitable. Guns had been developed in accordance with the new battlefield dynamic of close-engagement fighting; the British Sten, for instance, was utilitarian in design, basic in operation, easily dismantled for smuggling by resistance fighters, and used 9mm ammo that could be filched from Wehrmacht arsenals.

Toward the end of the war in 1945, 28-year-old Kalashnikov, himself a combat veteran from the Soviet tank corps, realised that there was a gap between the bulky bolt-action rifles and short-range sub-machine guns that had been the battlefield staples.

The Germans had, in the the StG (Sturmgewehr) 44, developed a kind of rifle/machine-gun hybrid that was supposed to be the first assault firearm – a selective fire (semi-auto and fully automatic) rifle (shoulder-fire capable) that used an intermediate cartridge and a detachable magazine that confirmed Kalashnikov's view that this class of weapon was what future conflicts would call for.

The AK-47 could not always shoot as far or as accurately as even other semi-automatic guns, and yet its build qualities and design attributes have ensured that it is still in demand and official production 65 years after it first saw active service. The Small Arms Survey 2004 estimated that out of the 500 million firearms available worldwide, between 70-100 million are of the AK family.

No shot in the dark

The AK was inspired by a compelling need supported by compelling evidence. As a combatant himself, Kalashnikov had first-hand experience of close-quarters ground fighting in the Second World War. Traditional rifles had effective firepower at up to 2,000m, but in combat situations the enemy rarely presented itself as such a target; rifles were also bulky and revealing where troops were fighting from concealed positions.

Sub-machine guns could spray a room with bullets, but the low-power calibre made them ineffectual for hitting targets beyond short ranges. They were also prone to jams because their intricate mechanism were sensitive to dust, heat and cold – the very conditions troops were encountering. The AK had to be robust, and the capability of functioning in extreme conditions was an integral aspect of its design ethos.

The AK was not the first gun to be conceived of with an existing type of cartridge – the M1943 round – but its overall specification was governed by the capabilities of this ammunition gauge; it also proved that medium-range bullets intended for machine guns could double as a single round when fired in semi-auto mode. Post-war constraints meant that Kalashnikov and his collaborators had limited R&D resources. However, the AK development programme was able to refine and modify prototypes to their satisfaction, and to test them against extreme operational conditions and situations that they were likely to encounter only rarely.

The AK's pressure-based repeat-fire system was not a new invention. Indeed the system – which harnessed pressure (caused by gas expelled from a discharging round) to drive back a spring-loaded bolt to simultaneously expel the empty cartridge, prompt a new cartridge to enter the firing chamber from the magazine, and also leave the bolt cocked for the next shot – had been introduced in the First World War with the M1918 Browning Automatic Rifle. This used a gas-operated long-stroke piston rod actuated by propellant gases bled through a barrel vent. Kalashnikov proved that this 30-year-old technology could be reworked for his hand-held assault rifle concept.

At the prototype stage, Kalashnikov and his co-developers looked to combine functions into fewer parts. An example of this (noted by Kalashnikov biographer CJ Chivers) was the combination of the gun's bolt carrier with its gas piston into one component, which brought the advantage that the combined weight added to the energy generated by each shot, which helped push out any accumulated grime or carbon.

One later modification was to redesign the AK's safety catch so that it doubled as protective cover to the bolt and area round the chamber that helped block alien bodies reaching the gun's innards. Although Kalashnikov's working aim was to reduce the number of working parts, he did not in the process want to make the parts smaller or more fragile, and thereby make them prone to damage or loss if the AK was being serviced under conditions of darkness or duress.

Counter intuitive engineering

Kalashnikov and fellow konstruktor (and ex-army engineer) Aleksandr Zaitsev, made AK prototype parts relatively loose-fitting, making the mechanism less likely to jam when it was dirty, under-lubricated, or carbon clogged from extended firing. According to CJ Chivers, this decision was counter-intuitive to most Western weapon designers accustomed to working with precision tools that allowed assembly lines to work within tight tolerances and to mill parts to exacting fit. Loose-fit also meant that the weapon could expand and contract when hot and cold without disaffecting its critical working parts. Principles of rigidity and give are, of course, basic to bridge and building architecture.

A downside of loose-fit is that the AK is reputed to be less accurate over longer distances (400m+) than other comparable guns – less of a problem with an assault rifle primarily intended for close-range engagement, but a problem if attempting to pick-off targets in the middle distance. Another concern with loose-fit is that when fired in automatic mode it can cause firers incognisant of this characteristic to worry that the weapon is shaking apart with each burst, resulting in a critical lapse in concentration amid combat situations.

The prescriptive nature of the Soviet NIPSMVO (Research and Proving Grounds for Firearms and Mortars) bureau arms development programme allowed sentimental attachments to past work; ideas that had taken weeks of R&D time were sometimes abandoned. 'Designers become affixed to a certain idea, and hesitate to discard it,' Kalashnikov has been quoted as saying. 'They are attached to their original concepts' like a spinster to her cats.'

The AK's bore and chamber, gas piston, and gas cylinder interior are generally chromium-plated: this enables these parts to resist corrosion and wear; doubly important, as much military-production ammo of the era contained potassium chlorate in the primers. This was converted on detonation to corrosive and hygroscopic potassium chloride. Chrome plating of critical parts is now commonplace to most military weapons.

Toward the end of its development period in late 1947, AK-47s were tested at NIPSMVO. Loaded prototypes were placed in swamp water, salt water, dragged through baths of sand, ash, rubble, stock-first, barrel-first, until all apertures were clogged. They were frozen; they were dropped onto concrete surfaces. As far as records reveal, each time the test weapons were retrieved, and the safety locks released, they fired. The loose-fit build and big operating parts were credited with this durability.

Although aesthetic considerations were not primary to the AK's design, it rather became the 'poster boy' of 20th century gun design. Its silhouette – the barrel mounted gas cylinder and 'banana-shaped' magazine – has become widely recognised, even iconic. The AK's distinctive 'clat-tat-tat' firing sound could also help distinguish between combatants in a dense cover firefight. *